This invention relates to an ink jet printhead. More particularly, this invention relates to a thermal ink jet printhead and an improved process for it""s fabrication.
Generally, the ink jet printing systems to which the subject invention relates are divided into either thermal ink jet type or bubble ink jet type. Typically, a thermal ink jet printhead is comprised of one or more ink-filled channels communicating with a small ink supply chamber at one end and having an opening at the opposed end, referred to as a nozzle. A thermal energy generator, usually a resistor, is located in each channel near the nozzle at a predetermined distance therefrom. The resistors are individually addressed with a current pulse to momentarily vaporize the ink and form a bubble. As the bubble grows, the ink bulges from the nozzle and is contained by the surface tension of the ink to form a meniscus. As the bubble begins to collapse, ink still in the channel between the nozzle and the bubble starts to move toward the collapsing bubble causing a volumetric contraction of the ink at the nozzle, resulting in separation of the bulging ink as a droplet. The acceleration of the ink out of the nozzle while the bubble is growing provides a momentum and velocity to the droplet in substantially a straight line in the direction of a recording medium, such as a sheet of paper. U.S. Pat. Nos. 4,463,359; 4,849,774 and 5,192,959 describe this type of system and are herein incorporated by reference.
A preferred technique for the manufacture of thermal ink jet printheads is the joining of two substrates, a first forming the ink channels and a second containing the heating electrodes to form a complete printhead. For example, U.S. Pat. No. Re. 32,572, herein incorporated by reference, discloses a method of forming a plurality of ink jet printheads of two silicon wafers. A plurality of sets of heating elements and their individually addressed electrodes are formed on a surface of one of the wafers and a corresponding plurality of parallel channels, each channel communicating with a manifold, are anistropically etched in a surface of the other wafer. A fill hole and alignment openings are etched in the opposed surface of the channeled wafer. Alignment marks are formed at predetermined locations on the wafer surface having the heating elements. The wafer surface with the channels is aligned with the heating elements via the alignment openings and alignment marks and the wafers are bonded together. A plurality of individual printheads are obtained by dicing the two aligned bonded wafers.
Each printhead is then fixedly positioned on the edge of an electrode or daughter board so that the channel nozzles are parallel to the daughter board edge. The printhead electrodes are wire-bonded to corresponding electrodes on the daughter board. The daughter board with printheads is mounted on an ink supply cartridge. Obviously, to function adequately, it is essential that each heating element and ink channel align precisely. As a review of the manufacturing process disclosed in the Re.32,572 patent will show, a primary emphasis in printhead manufacture is obtaining appropriate alignment of the individual component pieces.
Accordingly, it is a primary object of this invention to provide a new and improved thermal ink jet printhead.
It is an advantage of this invention to provide a new and improved printhead that is manufactured by a process which assures dependable alignment of a first ink channel substrate and a second heating element substrate.
Additional objects and advantages of the invention will be set forth in part in the description which follows and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the present invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing objects and in accordance with the purpose of the invention, as embodied and broadly described herein, the thermal ink jet printhead of this invention comprises a first ink channel containing substrate bonded to a second heating unit containing substrate wherein appropriate alignment of the heating units with their respective ink channels is achieved via cooperative key and keyway elements formed in the two substrates. The invention is applicable to both the printhead and the wafer scale. Moreover, the use of the key-keyway mating system can be used during the mating of wafers prior to any necessary dicing operation or may be used to mate the heater element and ink channel element of individual printheads.
In a preferred embodiment, the mating surfaces of the ink channel substrate and the heater unit containing substrate are substantially coplanar and include a first linear keyway channel, a second linear keyway channel perpendicular to the first, a first mating key ridge and a second mating key ridge perpendicular to the first, the key ridges being cooperative with the keyway channels.
In an alternative form, one of the substrates is formed to include lateral sidewalls or a rear wall which overlaps the corresponding sidewall of the other substrate and provides side-to-side and/or front to back alignment. This form of the invention can be used in addition to the keyway channel-key ridge elements or as a replacement therefore.
The inventive printhead of the present invention is manufacturable via a procedure comprising the steps of: (a) providing a first heating element substrate having at least one generally planar surface; (b) forming an array of heating elements on the planar surface and forming a pattern of electrodes on the substrate for enabling the individual addressing of each heating element; (c) depositing an insulation layer on the planar surface; (d) photo-patterning the insulating layer to expose the heating element; (e) forming an ink channel substrate having at least an ink reservoir and an ink channel; (f) forming a key on the ink channel substrate and a corresponding keyway on the heating element substrate to provide an alignment mechanism; and (g) adhesively securing the ink channel substrate to the heating element substrate using the alignment mechanism to achieve proper positioning of the ink channel(s) and heating elements.
In a particularly preferred form of the invention, the ink channel plate is a molded plastic piece formed according to the process comprising constructing a silicon preform of the desired shape, electroplating the silicon preform with a metal such as nickel to form a metal die, and molding the plastic channel substrate in the metallic die. This procedure is more fully described in U.S. Pat. No. 5,617,631, herein incorporated by reference.